This invention relates to a code division multiple access (CDMA) communication system and, in particular, to confinement of access from mobile terminals in such CDMA communication system.
A known CDMA communication system comprises a plurality of mobile radio terminals, a plurality of base stations having different radio service zones, and a base station control device. In a communication system, a particular one of the plurality of mobile radio terminals communicates with a particular one of the plurality of base stations having a particular one of the radio service zones in which the particular mobile radio terminal currently exists.
As is known in the art, the CDMA communication system uses a spread spectrum technique wherein a carrier signal is spectrum is spread, on a transmitting side, by use of a pseudo-noise (PN) code and is subsequently transmitted. On the receiving side, the transmitted signal is received as a received signal, which is, in turn, correlated with the PN code signal to derive the carrier signal from the received signal. In the CDMA communication system using the spread spectrum technique, many channels can be made by use of different PN codes, without use of different carrier frequencies, and can be protected from cross talk between each other as well as signal interception.
However, the CDMA communication system has graceful degradation, that is, that the communication quality degrades as the communication traffic or the number of calls increases. This means that a data communication requiring a high communication quality cannot be completed when the traffic increases excessively during the communication.
In order to resolve the problem of graceful degradation in the CDMA communication, JPA 5-145516 discloses provision of a memory for storing attributes of terminals accommodated in the system and maximum traffic values acceptable for attributes of the terminals to thereby control access of terminals to maintain the traffic by the terminals below the maximum traffic values.
According to the resolve by resolution of JPA 5-145516, it is undesirably required before using the system, to actually measure the radio transmission for various attributes of the terminals, such as telephone terminals, facsimile terminals, data transmission terminals and others within each of the radio service zones so as to determine the acceptable maximum traffic values.
Further, since the accessible maximum traffic values are fixedly determined for each of the attributes of the terminals, it is often impossible to efficiently use the frequency. This is because the accessible traffic values are dependent on traffic values and radio transmission conditions which always vary.